Phase structure, microstructure, and electrical properties of Sb-modified (K, Na, Li) (Nb, Ta) O3 piezoelectric ceramics

Lead-free (K0.44Na0.52Li0.04)(Nb0.80-xTa0.20Sbx)O-3 piezoelectric ceramics were prepared by the ordinary sintering method. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.00 to 0.06, the phase structure of the ceramics changed from the tetragonal to the pseudocubic phase, and both the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb5+ for Nb5+. By increasing x, the dielectric properties were optimized and the variation of dielectric constants before and after poling became smaller. Only the tetragonal-cubic phase transition was observed above room temperature in all the epsilon(r)-T curves. The degree of diffuseness increased from 1.29 at x=0.00 to 1.96 at x=0.06, indicating that the ceramics at x=0.06 changed to an approximate ideal relaxor ferroelectric. The temperature dependences of f(r) and k(p) became better by increasing x properly. Significantly, the ceramics with x between 0.00 and 0.04 had high density and outstanding electrical properties (d(33)=241-272pC/N, k(p)=0.42-0.52, epsilon(r)=1258-1591, tan delta=0.015-0.025, T-c=280 degrees-355 degrees C, E-c=10.62-12.60 kV/cm, and P-r=16.19-20.13 mu C/cm(2)). Besides, the underlying mechanism for variations of the electrical properties due to Sb5+ substitution was explained in this work.